In modern vehicle seats balloons which can be filled with a pressure medium, in particular with compressed air, are situated in a region of the seat or seat back (together designated as the seat bearing surface) as adjusting elements and can be supplied with pressure medium by means of a respective pressure medium line. As a result of filling a respective balloon with pressure medium, the volume thereof is increased such that, as a result, the characteristics of the contour of a seat back or seat are able to be modified. To fill the balloon with pressure medium, said pressure medium is initially generated from a pressure source, for example from a compressor, and is guided to a respective balloon via a corresponding valve, in particular an electro-pneumatic valve. In the case of said pneumatic systems, it is important here at the same time for the adjusting elements and valves, on the one hand, to be able to be matched finely to the requirements of the passenger. In addition, only limited installation space is available, as a rule, in automobile construction. This calls for the components of the pneumatic system to be designed in a filigree manner. Said design, however, holds the risk of, in particular, the pressure medium line easily being able to become clogged as a result of particles or even dust which is contained in the pressure medium.